Heretofore known methods and apparatus for grinding the sidewalls of tires and in particular the white sidewall areas thereof have had several limitations. It is ordinarly been necessary for an operator after placing a tire on the grinding apparatus, to movably position and manipulate the grinding wheel or wheels of the apparatus by handwheels to move the grinding wheels into engagement with the sidewall area to be ground. The quality of these prior art grinding machines depends totally upon a very precise setup by an expert technican. It also assumes that a very uniform tire is supplied to the grinder which is not totally correct whereby variations in the raised white sidewall area of the tire wall cause unevenness in sidewall grind. Due to the dimensional variations and inherent resilient characteristics of rubber, especially when in the form of an inflated pneumatic tire, it has been extremely difficult with known methods and apparatus to accurately set the grind depth on a mass production basis for uniform sidewall grinding. Even tires of the same nominal size are not always of uniform dimensions, with dimensions varying from tire to tire and even varying in different portions of the same tire.
In particular, it has been difficult to adjust and regulate the angle of the grinding wheel since the angle of the outer surface of the raised or recessed area will vary due to its location on the sidewall area of an inflated pneumatic tire. If the angle of the grinding wheel is not accurately adjusted too much material will be removed from one side of the raised or recessed sidewall area in order to remove sufficient material from the other side of the area resulting in a blemished tire or possibly a damaged tire if the depth of grind is excessive. Furthermore, if the grind depth and angle of the grinding wheel are not precise, the resulting exposed white rubber in the sidewall will appear distorted even if the grind depth is not excessive, providing a tire which must be sold as a blemished tire.
The controlled grinding of the sidewall area of pneumatic tires is generally required for three particular applications. The most common application is to remove an overlying layer of black rubber from an underlying raised area of white rubber to provide the standard raised annular white sidewall area that extends circumferentially about the sidewall of the tire. In other grind applications, the overlying black rubber is removed from raised letters to expose the underlying white rubber which defines the raised letters. Also, for certain tires the white rubber forming the white sidewall of the tire is at the bottom of an annular groove formed in the sidewall of the tire with the grinding wheel being required to remove the black covering rubber at the base of the groove to form a recessed white sidewall strip. Also, during the manufacture of some tires, the raised area which forms the annular portion of the tire for a usual white sidewall will be formed completely of black rubber which also requires grinding to remove the rubber flashing and to provide a uniform appearance to the raised black area thereof.
Various methods and apparatus have been proposed to overcome these problems and to provide a satisfactory and accurately controlled grind angle and depth of grind to eliminate the problems that have existed in the removal of the black covering rubber from the white sidewall areas of tires, whether the raised area is a circumferentially extending rib or raised spaced letters, or even an annular recessed area.
U.S. Pat. No. 2,707,851 shows an early prior art type of grinding machine in which the grinding wheels were manually adjusted by handwheels to regulate the angle of grind and depth thereof. U.S. Pat. No. 2,810,238 shows another prior art grinder in which the angular adjustment of the grind wheel is accomplished by handwheels and the location of the grinder is controlled by a roller which follows the contour of the tire tread. U.S. Pat. No. 2,893,712 shows a grinding wheel in which the grind angle and depth are controlled by manually operated handwheels thereby relying on the expertise of the operator to achieve a satisfactory removal of the black covering rubber. U.S. Pat. No. 2,986,849 shows another sidewall grinder in which the grinding pressure on the grinding wheel is controlled by pivoting the grinder on the end of an arm with the depth being controlled by a roller which rolls along a predetermined sidewall area of the tire.
Other prior art sidewall grinders for penumatic tires have attempted to compensate for the varying angle of the top surface of the raised sidewall area by constraining the sidewall area of the inflated tire whereby the top surface of the raised sidewall area will be generally flat in relationship to the plane of the tire equator. This wi11 enable the grinding wheel to engage the raised area perpendicularly to eliminate any angle in the raised sidewall area. Examples of such apparatus are shown in U.S. Pat. Nos. 3,077,060 and 3,137,976. U.S. Pat. No. 3,128,579 shows another white sidewall grinding apparatus which initially adjusts the grinding wheels by manually operated handwheels and then provides an automatic adjustment control by a contour regulator wheel which engages the rib on the sidewall to insure that the grinding wheels follow the contour of the tire. Although this construction attempts to compensate for irregular contour in the sidewall, it does not provide for directly measuring the angle of the raised white sidewall area and then regulating the grind angle accordingly.
U.S. Pat. Nos. 3,172,243; 3,290,831; and 3,521,480 attempt to solve the problem of grinding the desired amount of covering material from the raised white sidewall area made difficult by the angular variation of the top surface of the raised area in the sidewall, by positioning the sidewall surface in a relatively flat horizontal plane when inflated in the grinding machine to insure an even depth of grind upon perpendicular contact of the grinding wheel against the raised sidewall area.
Although it has been recognized in the sidewall grinding art, that problems are presented by the angularity of the top surface of the raised area of sidewall material, most known prior art grinding apparatus have attempted to solve this problem by accurately adjusting the angle of the grinding wheel manually during the grinding operation which relies upon the skill of the operator. Alternatively, this problem has been attempted to be corrected by flatting the sidewall area of the tire when mounted in the grinder by restraining the sidewall area by steel plates, with the subsequent anticipation that the raised area will be perpendicular to the moving grinding wheel.
Therefore, the need exists for an improved sidewall grinding apparatus and method which eliminates the reliance on the skill of the operator for achieving a satisfactory and accurate removal of the covering material and a portion of the underlying sidewall material which usually will be a contrasting color to the black rubber of the sidewall, and which avoids the necessity of flatting the sidewall area of the tire by steel retention plates when in the grinder to compensate for any angularity in the raised area.